1. Field of the Invention
The present invention generally relates to a cooling fan and, more particularly, to a centrifugal cooling fan.
2. Description of the Related Art
Conventional cooling fans include axial-flow fans and centrifugal fans. The axial-flow fan has an axial air inlet and an axial air outlet opposite to the axial air inlet. Air can be drawn into the fan via the axial air inlet and then expelled from the fan via the axial air outlet. The centrifugal fan has an axial air inlet in an axial direction and a radial air outlet in a radial direction of the fan. Air can be drawn into the fan via the axial air inlet and then expelled from the fan via the radial air outlet for cooling purposes.
Since the axial-flow fan expels air only in the axial direction rather than in the radial direction, the axial-flow fan must be mounted on the top of an electronic device to be cooled, such as a Central Processing Unit (CPU) of a computer. As a result, the height of the electronic device cannot be reduced.
In addition, since the centrifugal fan is able to expel air via the radial air outlet, it is not required to mount the centrifugal fan on the top of the heat source. Advantageously, it allows the centrifugal fan to be installed in various electronic devices with limited interior spaces (such as mobile phones, notebook computers, PDAs, etc). However, when the centrifugal fan is installed in the electronic device, foreign debris (such as dust or water) may enter the centrifugal fan via its axial air inlet, resulting in damage to the fan.
In light of this problem, Taiwan Patent No. I330224 discloses a centrifugal fan 9 as shown in FIG. 1. The centrifugal fan 9 includes a fan frame 91 having an axial air inlet 911 and a radial air outlet 912. The fan frame 91 receives an impeller and a stator assembly that is used to drive the impeller to rotate.
The centrifugal fan 9 may be installed in an electronic device 90 having a frame 901 and a partitioning wall 902. A lateral air passage “S” may be formed between the fan frame 91 and the partitioning wall 902. When the stator assembly drives the impeller to rotate, air can be drawn into the lateral air passage “S” via an air inlet of the frame 901. In the electronic device 90, air is drawn into the centrifugal fan 9 via the axial air inlet 911 and expelled from the fan 9 via the radial air outlet 912. Based on this, the fan 9 is able to output air currents to the heat source for cooling purposes.
Since the lateral air passage “S” is provided for air to smoothly flow into the fan 9 via the axial air inlet 911, the impeller of the fan 9 will not be able to guide sufficient air into the fan 9 via the lateral air passage “S” if the space between the fan frame 91 and the partitioning wall 902 is insufficient. As a result, the amount of air flowing into the fan 9 will be limited, affecting the cooling effect of the fan 9. The service life of the electronic device 90 is even shortened.